Calibration-Free Terahertz Characterization of Thin Films on Dielectric Boards by Free-Space Transmission and Reflection Coefficients

The study of electromagnetics and its applications has gained growing importance across numerous scientific and technological fields. Accurate material characterization, partic ularly of multilayered structures, is essential for the effective design of electronic, optical, and construction systems. This article proposes a novel calibration-free method to characterize thin films or coatings on dielectric boards using free-space transmission and reflection measurements at terahertz (THz) frequencies for the first time. Unlike conventional approaches for three-layer materials, the proposed method eliminates the need for reference-plane calibration and accurate size manufacture of samples, thereby reducing system complexity, especially at THz bands. Extensive simulations validate the method’s performance across varying material thicknesses and loss tangents, demonstrating strong applicability for common materials. Experimental application in the 220–330-GHz range further confirms its precision in permittivity estimation, highlighting the method as a promising tool for THz permittivity characterization.